Various manufacturing processes involve the large-scale removal of water from a cellulose product to form an end product. Specifically with reference to the paper industry, conventional manufacturing methods utilized involve a variety of steps ultimately designed to reduce the water content of a fiber sheet down to a level where the final paper product will have the desired performance characteristics. For instance, with paper that contains recycled fibers, one process for its manufacture begins with a slurry of cellulose product containing waste corrugated medium and water. As can be understood, virgin fibers may also be used in the slurry, with or without recycled fibers. The slurry is then blended and put through a head box, which applies heat and pressure and lays the resulting intermediate paper product down onto a conveyor screen generally in the form of a continuous sheet. The intermediate paper product may be conveyed through various drying stages where additional heat and air currents are used to drive the moisture out of the product.
At one or more stages of the paper forming process, a vacuum draw may be applied to the intermediate paper product or sheet to aid in moisture extraction. One example of such a stage is when the paper sheet is conveyed over a perforated roller that applies tension to wring the liquid moisture out of the sheet. The moisture is carried away by the vacuum draw into the center of roller and then onto a chamber where the liquid level builds up. Emptying the chamber of the liquid moisture in a vacuum pressure environment generally lower than the pressure of the surrounding ambient environment (e.g., atmospheric pressure) is difficult. The mechanical device drawing the vacuum to carry air or other gases and liquid moisture from the sheet is typically not designed to process the liquids, thus necessitating the intermediate storage chamber for the liquids. At the same time, the liquid cannot build up indefinitely in the chamber, and because the chamber is at negative pressure to the ambient environment, it cannot simply be passively drained. In fact, if too much liquid is maintained in the chamber, it will affect the ability of the vacuum to draw additional moisture out of the paper sheet, leading to variations in the moisture content and weight of the final product, which are undesirable.
One solution for the removal of the accumulating liquid is to utilize a pump (e.g., a centrifugal pump) connected with a liquid outlet of the chamber to pump the liquid to another location outside of the vacuum environment. These pumps, however, are inherently put under significant stress in extracting liquid from a negative relative pressure environment. Common problems encountered in pumping in a vacuum include premature failure of packing and mechanical seals, as well as air locking. Furthermore, such pumping requires a significant amount of energy, which increases the cost of the paper manufacturing process. In view of these disadvantages, a vacuum system could be implemented to draw in both gases and liquid. Such vacuum systems are more complex than a vacuum system that merely handles gases, though, and also require significantly more energy to operate.